Conventionally, many seamless capsules used for a medicine or the like are manufactured by a so-called dropping method. The dropping method is carried out by using a multiple nozzle. Thus, in the case of manufacturing a two-layer capsule, a double nozzle having an ejection port for ejecting the capsule filling substance and an ejection port for ejecting the film forming substance respectively arranged at the inside and at the outside is used. The filling substance and the film forming substance are ejected from the tips of the respective nozzles into hardening liquid, and the ejected liquid drops take a spherical form due to the surface tension thereof. Then, the liquid drops are cooled and hardened in the hardening liquid that is forced to circulate at a constant speed to make spherical seamless capsules.
As such a seamless capsule manufacturing apparatus, those disclosed in, e.g., Patent Documents 1 to 3 have been proposed. Patent Document 1 discloses a seamless capsule manufacturing apparatus using a multiple nozzle provided with a vibration unit. In the apparatus of Patent Document 1, liquid flow for forming capsule is allowed to be ejected from the multiple nozzles into hardening liquid. Jet liquid flow formed in the hardening liquid is cut by means of vibration to thereby form a multilayer seamless capsule. More specifically, a vibration unit is arranged at a diaphragm-shaped flexible part provided at the upper portion of the nozzle. Vibration is applied to the nozzle using the vibration unit to divide the jet liquid flow in the hardening liquid into multilayer droplets. The multilayer droplet is moved in the hardening liquid together with the liquid flow. Then, the external layer of each droplets are hardened to form a multilayer seamless capsule.
Patent Document 2 discloses a seamless capsule manufacturing apparatus that applies intermittent flow of coolant in a regular manner to jet flow of capsule forming liquid which is ejected from a multiple nozzle from the side periphery of the jet flow to thereby form a multilayer seamless capsule. In the apparatus of Patent Document 2, the capsule forming liquid is supplied from a liquid storage tank to the nozzle by means of a liquid feed pump and is ejected from the nozzle as jet flow. The jet flow is divided by means of impact of the intermittent flow of the coolant into small multilayer droplets, each of which is hardened in the coolant to become a multilayer seamless capsule. Patent Document 3 discloses a seamless capsule manufacturing apparatus that directly vibrates the nozzle so as to form a multilayer seamless capsule. In the apparatus of Patent Document 3, the flexible part as provided in the apparatus of Patent Document 1 is not provided in the nozzle, but a vibration unit provided at the upper portion of the nozzle is used to directly apply vibration to the nozzle.    Patent Document 1: Japanese Patent No. 3361131    Patent Document 2: Jpn. Pat. Appln. Publication No. 04-067985    Patent Document 3: Jpn. Pat. Appln. Laid-Open Publication No. 59-112831
Meanwhile, in such a seamless capsule manufacturing apparatus, capsule forming liquid is generally supplied from a liquid storage tank to the nozzle by a liquid feeding unit provided with a liquid feeding pump. The liquid storage tank and nozzle are connected to each other by a liquid feeding tube. That is, the capsule forming liquid is supplied to the nozzle through the liquid feeding tube by the operation of the liquid feeding pump. However, in such a seamless capsule manufacturing apparatus, when the liquid feeding pump is activated, vibration occurs in the liquid feeding unit. This vibration is transmitted to the liquid feeding tube to thereby vibrate the tube itself. When the liquid supply tube vibrates the vibration is transmitted to the nozzle, with the result that the vibration is superposed on (added to) the jet flow ejected from the nozzle.
When vibration is applied to the nozzle as in the case of the apparatus disclosed in Patent Documents 1 and 3 in a state where the vibration is superposed on the jet flow, it causes a problem in that vibration other than the vibration applied by the vibration unit is added to the jet flow as noise. When a noise component other than the vibration unit is added to the vibration added to the jet flow, a nonuniform liquid layer may be caused or droplet diameter may become nonuniform, causing problems, such as casing eyes of the seamless capsule, uneven thickness thereof, or variation in the particle diameter thereof.
In contrast, in the apparatus disclosed in Patent Document 2, an accumulator for alleviating minute pulsating flow of the liquid to be supplied is provided between the pump and nozzle so as to keep the nozzle inner pressure substantially constant. However, this configuration does not prevent the vibration generated in the pump from being transmitted to the nozzle. Thus, a problem of the noise vibration cannot be solved.
On the other hand, in the apparatus disclosed in Patent Document 3, a flexible portion for absorbing the vibration of the nozzle is provided in the middle of the liquid feeding tube so as to prevent the vibration of the nozzle from being transmitted to the pump side. This configuration eventually allows the vibration generated in the pump to be absorbed at this flexible portion. However, the flexible portion disclosed in Patent Document 3 aims to prevent an adverse effect caused due to application of the vibration to the nozzle itself and is an adapter-type member attached to the connection portion between the liquid feeding tube and nozzle. An experiment conducted by the present inventor reveals that it is impossible to sufficiently prevent transmission of the vibration generated on the liquid feeding unit side only by attaching the adapter-type small member to the pipe sleeve. In addition, the influence that the vibration generated on the liquid feeding unit side gives to the nozzle is far greater than the influence that the vibration generated on the nozzle gives to the pump and is directly linked to product quality.
An object of the present invention is to prevent the vibration generated on the liquid feeding unit side from being transmitted to the nozzle in the seamless capsule manufacturing apparatus so as to reduce vibration noise at the time of capsule formation thereby stabilizing product quality.